span.sig_valid {
    background: #dfffe6 url(pix/lock.png) no-repeat scroll right top;
    padding: 1px 18px 1px 0;
}

span.sig_invalid {
    background: #ffafaf url(pix/lock_break.png) no-repeat scroll right top;
    padding: 1px 18px 1px 0;
}